Method and machine for manufacturing a fibre electrode

ABSTRACT

A method for forming a connection such as an electrical connection, to a fiber material electrode element comprises moving a length of the fiber material relative to a pressure injection stage and pressure impregnating by a series of pressure injection pulses a lug material into a lug zone part of the fiber material to surround and/or penetrate fibers of the fiber material and form a lug strip in the lug zone. The fiber material may be a carbon fiber material and the lug material a metal such as Pb or a Pb alloy. Apparatus for forming an electrical connection to a fiber material electrode element is also disclosed.

FIELD OF THE INVENTION

The invention relates to an improved method and machine for forming aconnection, particularly an electrical connection, to a fibre material,particularly a fibre material, for use in general as an electrodematerial, such as for a battery or cell fibre electrode, and to amaterial so formed, particularly an electrode so formed.

BACKGROUND

In a lead-acid battery or cell comprising a fibre particularly carbonfibre electrode or electrodes, typically a very low electricalresistance and mechanically durable connection is required between theconductive fibre electrode material and a connector or lug (hereingenerally referred to as lug) to the external circuit.

Our PCT international patent application discloses a method for forminga lug on an electrically conductive fibre material electrode elementwhich comprises pressure impregnating lug material typically in a die,to surround and/or penetrate fibres of the fibre material.

To enable fast high volume manufacture of multiple electrodes some formof continuous lug forming process is required.

SUMMARY OF INVENTION

In broad terms in one aspect the invention comprises a method forforming a connection to a fibre material electrode element, whichcomprises moving a length of the fibre material relative to a pressureinjection stage or vice versa and by the pressure injection stagepressure impregnating by a series of pressure injection pulses a lugmaterial into a lug zone part of the fibre material to surround and/orpenetrate fibres of the fibre material and form a lug strip in the lugzone.

In broad terms in another aspect the invention comprises a method forforming an electrical connection to an electrically fibre materialelectrode element, which comprises moving a length of the fibre materialrelative to a pressure injection stage or vice versa and by the pressureinjection stage pressure impregnating by a series of pressure injectionpulses an lug material into a lug zone part of the fibre material tosurround and/or penetrate fibres of the fibre material and form a lugstrip in the lug zone, electrically connected to the fibre material.

In broad terms in another aspect the invention comprises a method forforming an electrical connection to an electrically conductive fibrematerial electrode element, which comprises moving a length of theconductive fibre material relative to a pressure injection stage or viceversa and by the pressure injection stage pressure impregnating by aseries of pressure injection pulses an electrically conductive lugmaterial into a lug zone part of the fibre material to surround and/orpenetrate fibres of the fibre material and form a lug strip in the lugzone, electrically connected to the fibre material.

In at least some embodiments the pressure impregnating comprisespressure impregnating without containing the lug zone part of the fibrematerial in a die (sealed or not)

In broad terms in another aspect the invention comprises a method forforming an electrical connection to a fibre material electrode element,which comprises moving a length of the fibre material relative to apressure injection stage or vice versa and by the pressure injectionstage pressure impregnating without containing the lug zone part of thefibre material in a die a lug material into a lug zone part of the fibrematerial to surround and/or penetrate fibres of the fibre material andform a lug strip in the lug zone, electrically connected to the fibrematerial.

In broad terms in another aspect the invention comprises a method forforming a connection to a fibre material electrode element, whichcomprises moving a length of the fibre material relative to a pressureinjection stage that applies continuous pressure to the electrodeelement or vice versa and by the pressure injection stage continuouslyimpregnating a material into the lug zone part of the fibre material tosurround and/or penetrate fibres of the fibre material and form a lugstrip in the lug zone, connected to the fibre material.

In broad terms in another aspect the invention comprises a method forforming an electrical connection to an fibre material electrode element,which comprises moving a length of the fibre material relative to apressure injection stage that applies continuous pressure to theelectrode element or vice versa and by the pressure injection stagecontinuously impregnating an lug material into the lug zone part of thefibre material to surround and/or penetrate fibres of the fibre materialand form a lug strip in the lug zone, electrically connected to thefibre material.

Typically the method comprises moving the fibre material continuously orin a stepped movement, and by the pressure injection stage pressureimpregnating lug material into the lug zone part of the fibre materialby the series of pressure injection pulses during the relative movementbetween the fibre material and pressure injection stage so that multiplepressure injection pulses inject lug material into different adjacentportions of the fibre material but forming a continuous lug along thelug zone.

The method of the invention may require that the series of pressureinjection pulses are a controlled series of pressure injection pulses.

The method of the invention may be carried out without containing thelug zone part of the fibre material in a die.

The length of the fibre material can be subsequently cut across the lugstrip to form multiple individual electrode elements each with a lug forexternal connection of the electrode element.

In at least some embodiments the continuous lug has a width along theplane of the material in the range about 1 mm to about 200 mm and thepressure impregnating comprises delivering the lug material into thefibre material from an orifice of an area in the range about 0.1 toabout 10 mm².

In at least some embodiments:

-   -   the pressure impregnation comprises delivering the lug material        into the fibre material from an orifice in contact with a        surface of the fibre material or spaced not more than 2 mm from        the surface of the fibre material, and/or    -   a duration of each pressure injection pulse is in the range        about 0.1 to about 2 seconds, and/or    -   the rate of relative movement between the fibre material and        pressure injection stage is in the range about 0.01 m/s to 10        m/s, and/or    -   the volume of each pressure injection pulse delivered by each        individual orifice is <1 cm3, and/or    -   a temperature differential exists between the lug material at        injection and the fibre material eg. the temperature at        injection is between about 300° C. to about 500° C. and the        temperature of the fibre material is less than 300° C., and/or    -   the frequency of pressure pulses is at least 1 Hz, and/or    -   the lug material when delivered by the series of pressure pulses        comprises a contiguous strip of lug material that may be        electrically and/or mechanically connected, and/or    -   the series of pressure pulses can be delivered at a rate in the        range of 1 pulse/0.1 m to about 200 pulses/0.1 m.

In at least some embodiments the pressure of each pressure injectionpulse is higher at or towards an end of the pulse than at or towards astart of each pulse.

In broad terms in another aspect the invention comprises a fibrematerial having a length of at least 1 meter with a lug strip along alength of the fibre material and having a width less than a width of thefibre material, comprising a continuous impregnation of a lug materialinto the fibre material surrounding and/or penetrating and electricallyconnecting to the fibres of the fibre material.

The fibre material may have a length of at least 10 meters.

The lug strip may be formed at or near a length-wise edge of the fibrematerial and comprising a lug extension beyond an edge of the fibrematerial.

Typically the fibre material is a non-metallic material such as a carbonfibre material, such as a non-woven such as fluid-entangled carbon fibrematerial, felted carbon fibre material, or a knitted or a woven carbonfibre material. The material has an average interfibre spacing less thanabout 250 microns and in some embodiments less than about 200, less thanabout 100 microns, less than about 50 microns, less than about 20microns, or less than about 10 microns.

In some embodiments the impregnating material impregnates between atleast about 30%, at least about 40%, at least about 50%, at least about70%, at least about 80%, or at least about 90%, or at least about 95%,or at least about 98%, or at least about 99% of the fibres.

In all embodiments above the fibre material may be a non-woven materialsuch as a felt material, a woven material (comprising intersecting warpand weft fibres), or a knitted material. The material may be a carbonfibre material, such as a non-woven, knitted, or woven carbon fibrefabric, or alternatively a glass fibre or silicon based fibrousmaterial. The fibres, for example, carbon fibres are typicallymultifilamentary but may be monofilament. In some embodiments the fibrematerial has an average interfibre spacing of less than about 250microns, or less than about 200 microns, less than about 100 microns,less than about 50 microns, less than about 20 microns, or less thanabout 10 microns. The fibre diameter may be in the range from about 1micron to about 30 microns, from about 4 microns to about 20 micron,from about 5 microns to about 15 microns. The voidage in the(unimpregnated) material may be at least about 50%, or at least about60%, or at least about 70%, or at least 80% or at least about 95%, or atleast about 98%, or at least about 99% for example.

In some embodiments the impregnating lug material is a metal. In oneembodiment the metal is Pb or a Pb alloy (herein both referred toinclusively as Pb). In another embodiment the metal is a Zn or a Znalloy (herein both referred to inclusively as Zn). In another embodimentthe metal is Cd or a Cd alloy (herein both referred to inclusively asCd). In another embodiment the metal is Al or a Al alloy (herein bothreferred to inclusively as Al). Alternatively the impregnating lugmaterial may be a polymer material such as a conductive polymer forexample.

In some embodiments the fibre material may be carbon fibre materialwhich has been treated by electric arc discharge. The carbon fibrematerial may be electric arc treated by moving the carbon fibre materialwithin a reaction chamber either through an electric arc in a gapbetween electrodes including multiple adjacent electrodes on one side ofthe material, or past multiple adjacent electrodes so that an electricarc exists between each of the electrodes and the material. In otherembodiments the carbon fibre material for use as the electrode currentcollector material may be thermally treated at an elevated temperaturefor example in the range 1200 to 2800° C. Such treatment may increaseelectrical conductivity of the material.

In a cell or battery, the positive electrode or electrodes, the negativeelectrode or electrodes, or both, may be formed of one or more layers ofthe fibre material with a lug, in accordance with the invention. Theinvention has been described herein sometimes with reference toelectrodes of lead-acid (Pb-acid) batteries but may also haveapplication to other battery types such as Li-ion batteries, and inother applications such as in electrodes in solar cells, or incapacitors or supercapacitors, for example.

In some embodiments the invention comprises a hybrid automotive vehiclecomprising a Pb-acid battery of the invention and/or made in accordancewith the methods taught herein. In other embodiments the hybridautomotive vehicle has stop-start and/or regenerative brakingfunctionality. In other embodiments the battery can carry accessoryloads when the vehicle engine is off.

A benefit of the manufacturing method and product of the invention isthat the continuous fibre material which is subsequently cut toindividual electrodes, has formed thereon a continuous lug strip ratherthan a series of individual separated lug segments. This continuous lugstrip acts to strengthen continuous fibre material during subsequentmanufacturing steps and handling, such as pasting with active material,carried out before the continuous fibre material is then cut intoindividual separated electrodes. The presence of the continuous lugalong the continuous fibre material rather than a series of individualseparated lug segments may also make it easier to feed the continuousfibre material through subsequent manufacturing steps.

In broad terms in a further aspect the invention comprises apparatus forforming an electrical connection to a fibre material electrode element,arranged to move a length of the fibre material relative to a pressureinjection stage or vice versa and by the pressure injection stagepressure impregnating by a series of pressure injection pulses a lugmaterial into a lug zone part of the fibre material to surround and/orpenetrate fibres of the fibre material and form a lug strip in the lugzone.

In broad terms in a further aspect the invention comprises apparatus forforming an electrical connection to an electrically conductive fibrematerial electrode element, arranged to move a length of the conductivefibre material relative to a pressure injection stage or vice versa andby the pressure injection stage pressure impregnating by a series ofpressure injection pulses an electrically conductive lug material into alug zone part of the fibre material to surround and/or penetrate fibresof the fibre material and form a lug strip in the lug zone, electricallyconnected to the fibre material.

In board terms in a further aspect the invention comprises apparatus forforming an electrical connection to a fibre material electrode element,arranged to move a length of the fibre material relative to a pressureinjection stage or vice versa and by the pressure injection stagepressure impregnate by a series of pressure injection pulses a lugmaterial into a lug zone part of the fibre material to surround and/orpenetrate fibres of the fibre material and form a lug strip in the lugzone, electrically connected to the fibre material.

In some embodiments the apparatus is arranged to form the lug strip ator near a length-wise edge of the fibre material. In some embodimentsthe apparatus is arranged to form the lug strip transversely across thefibre material. In some embodiments the lug strip further includes a lugextension or extensions beyond the edge of the fibre material. In someembodiments the lug extension(s) may be cut out of the lug strip forexample by stamping.

In some embodiments the apparatus is arranged to move the fibre materialrelative to the pressure injection stage or vice versa by carrying thefibre material on a heat sink conveyor. In some embodiments the heatsink conveyor comprises a rotating drum and the fibre material passesthrough a nip between the rotating drum and the pressure injectionstage.

In this specification ‘lug’ means any electrically conductive element orconnector which enables external connection of the fibre electrode,regardless of physical or mechanical form.

In this specification ‘lug region’ and ‘lug zone’ are usedinterchangeably and have the same meaning and refers to a region of thefibre material which after forming of a lug comprises a matrix of lugmaterial encapsulating the fibre material, and optionally the lug zonemay also include an extension of solid lug material continuously or atintervals to a side of this matrix.

In this specification “matrix” in relation to the lug refers to lugmaterial encapsulating the fibre material in the lug zone in a3-dimensional structure that has length, width and depth.

In this specification “hybrid vehicle” refers to a vehicle thatincorporates any one of idle elimination (stop-start functionality),regenerative braking, and any combination of an internal combustionengine with an electric motor where one or the other or both can providea drive functionality, a hybrid vehicle may also include a vehicle thatmay only be a partial hybrid vehicle.

More generally the method of the invention may be used for forming anelectrical connection to a fibre material which is not an electrodeelement, or even more generally for impregnating a first material whichis not also electrically conductive, into a fibre material not forforming an electrical connection to the fibre material but instead forother industrial purposes, and thus more broadly than described abovethe invention may be said to include a method for forming an integralarea of a first material in and through a thickness of a second, fibrematerial, which comprises moving a length of the fibre material relativeto a pressure injection stage or vice versa and by the pressureinjection stage pressure impregnating by a series of pressure injectionpulses the first material into a part of the area of the fibre materialto surround and/or penetrate fibres of the fibre material and to form anarea of the impregnated material in the fibre material.

In broad terms in a further aspect the invention comprises a method forforming an integral area a first material in and through a thickness ofa larger area of a second, fibre material, which comprises moving alength of the fibre material relative to a pressure injection stage orvice versa and by the pressure injection stage pressure impregnating(without containing the fibre material in a die) the first material intoa part of the area of the fibre material to surround and/or penetratefibres of the fibre material and to form an area strip of theimpregnated material in the fibre material.

Additionally the method of the invention may be used to increase thetensile strength of the fibre material along the fibre materials lengthand width making it stronger than it would otherwise be without.

The term “comprising” as used in this specification means “consisting atleast in part of”. When interpreting each statement in thisspecification that includes the term “comprising”, features other thanthat or those prefaced by the term may also be present. Related termssuch as “comprise” and “comprises” are to be interpreted in the samemanner.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention are further described with reference to theaccompanying figures by way of example wherein:

FIG. 1 shows carbon fibre material electrode with a Pb lug formed by amethod embodiment of the invention,

FIG. 2 is schematic cross-section of an electrode comprising multiplelayers of carbon fibre material and a lug,

FIG. 3 is schematic cross-section of an electrode similar to that ofFIG. 2 but comprising a single layer of carbon fibre material and a lug,

FIG. 4 shows a schematic of a portion of carbon fibre material with a Pblug strip being formed on it in close up,

FIG. 5 is a schematic cross-section view of carbon fibre materialpassing beneath a pressure injection head,

FIG. 6 is a schematic cross-section view of a pressure injection stage,

FIG. 7 is a schematic plan view of fibre material entering and exiting apressure impregnation stage in an embodiment for forming a singlelengthwise edge lug strip,

FIG. 8 is a schematic plan view of fibre material entering and exiting apressure impregnation stage in another embodiment for forming lug stripsalong both lengthwise edges,

FIGS. 9A and 9B are images of the top side and underside of a section ofcarbon fibre felt with a Pb lug strip formed therein as described in theexperimental examples,

FIGS. 10A and 10B are images of the underside and top side of part of aPb lug strip (alone) formed on a carbon fibre felt as described in theexperimental examples,

FIG. 11 is an SEM image of the underside of part of a Pb lug stripformed on a carbon fibre felt,

FIG. 12A is an SEM image of a cut through the Pb lug strip (alone)formed on carbon fibre felt,

FIG. 12B is a higher magnification SEM image than FIG. 12A showing Pbimpregnating around and between individual fibres with low voidage,

FIG. 13 is a perspective view of an embodiment of a lug forming machine,

FIG. 14 is a side view of the lug forming machine of FIG. 13.

FIG. 15 is a schematic vertical cross-section view of the lug formingmachine along line II-II of FIG. 13,

FIG. 16 is an enlarged schematic vertical cross-section view along lineII-II of FIG. 13 of an injector head, enlarged to show operating partsin greater scale,

FIG. 17 is a side view of the lug forming machine along line of FIG. 13,

FIG. 18 is a schematic vertical cross-section view along line of FIG. 13of the injector head of FIG. 16, enlarged to show operating parts ingreater scale,

FIG. 19 is an enlarged schematic vertical cross-section view similar tothat of FIG. 16 but of an alternative embodiment of an injector head,and

FIG. 20 is an enlarged schematic vertical cross-section view similar tothat of FIG. 18 but further enlarged, of the alternative embodimentinjector head of FIG. 19 of injector 201/202.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Lugs

FIG. 1 shows a section of a conductive fibre electrode such as of carbonfibre, for a Pb-acid cell or battery for example, with one form of lugsuch as a Pb lug, formed on the fibre material by a pressureimpregnating embodiment of the invention. The fibre material isindicated at 1 and the lug at 2. The lug may have a similar thickness(dimension through the plane of the material) to the fibre materialthickness (single or multiple layers) or a lesser thickness, or may beof greater thickness. FIG. 2 is a schematic cross-section of a similarelectrode indicating both a lug zone 50 and electrode zone 51. Theelectrode in FIG. 2 comprises multiple layers 1 of fibre material, and alug 2. FIG. 3 is schematic cross-section of an electrode similar to thatof FIG. 2 but comprising a single layer of carbon fibre material and alug. In the embodiments shown the lug has a lug extension 3 beyond theedge of the fibre material, comprising lug material only ie solid lugmaterial such as Pb. The lug is typically formed of metal such as Pb ora Pb alloy, Zn or a Zn alloy, or Cd or a Cd alloy, or Al or a Al alloy,but may alternatively be formed of other lug material such as aconductive polymer for example.

In the embodiment shown the lug extends along a single edge of theelectrode, which is a single upper edge, but alternatively the lug mayextend along two or more edges of the electrode, the lug may be curvedor arcuate (arched) in shape, and/or may be formed to extend across acentre area of an electrode and/or the electrode zone. Additionally atransverse/macro-scale current collector 52 may be provided that isformed in the same way as the lug as will be described, that extendsfrom the lug zone across and to any location within the electrode zone.Preferably the macro scale current collector extends to the edge of theelectrode diametrically opposite the lug zone.

In some embodiments substantially all or at least a majority of thefibres of the electrode material extend continuously across theelectrode to or through the lug.

The fibre material may be a non-woven such as fluid-entangled, felted,knitted, or woven fibre fabric, in particular a non-woven such as afluid-entangled, felt, knitted, or woven carbon fibre fabric.Alternatively the material may be a glass fibre or silicon based fibrousmaterial, which may be coated with a conductive material typicallymetal, such as a Pb film or coating. The fibres, for example carbonfibres, are typically multifilamentary but may be monofilament. In atleast some embodiments the fibre material has an average interfibrespacing of less than about 250 microns, less than about 100 microns,less than about 50 microns, less than about 20 microns, or less thanabout 10 microns. In at least some embodiments the fibre diameter is inthe range from about 1 micron to about 30 microns, from about 4 micronsto about 20 micron, or from about 5 microns to about 15 microns. Thevoidage in the (unimpregnated) material may be in the range of fromabout 50% to at least about 99%, from about 40% to about 99%, or fromabout 30% to about 98%, or from about 20% to about 98%, or from about15% to about 98%, or from about 10% to about 95%. This voidage of theunimpregnated material being the space (voidage) not occupied by thefibres of the fibre material.

In some embodiments the impregnating material impregnates between atleast about 50%, at least about 60%, at least about 780%, or at leastabout 80%, or at least about 90, or at least about 95%, or at leastabout 98% of the voidage fibre material. This voidage of theunimpregnated material, being the space (voidage) not occupied by thefibre material itself or the impregnating material that has impregnatedthe fibre material, i.e., this is the voidage remaining of theunimpregnated material after it has been impregnated.

In some embodiments the interfibre voidage in the fibre material (beingthe fraction of the total volume defined by the material outsidedimensions not occupied by the fibres—in the unimpregnated material) isreduced by impregnation of the lug material between into the interfibrevoidage between the fibres to, at least about 50%, at least about 70%,at least about 80%, at least about 90%, at least about 95%, at leastabout 98%, or at least about 99% of the original interfibre voidage.

In some embodiments the fibres of the fibre material are multifilamentfibres and the impregnating lug material also penetrates betweenfilaments also reducing intrafibre voidage. In some embodimentsintrafibre voidage is also reduced to about 40%, to about 30%, to about25%, to about 20%, to about 10%, to about 5%, or to about 1% of theintrafibre voidage in the unimpregnated fibre material.

A matrix of the lug material encapsulates the microscale carbon fibreelectrode material in the lug zone. A very low electrical resistanceconnection is formed between the microscale carbon fibre electrodematerial and lug. Also voidage between the lug material and the fibresis minimised, preventing or minimising battery electrolyte fromsubsequently entering the lug to fibre connection and deteriorating theconnection, so the connection is more durable.

Optionally any remaining (open cell/porous) voidage between the lugmaterial and the fibres and/or filaments may be reduced by filling witha material which is substantially inert to the electrolyte, such as forexample a non-conductive polymer such as an epoxy.

Optionally the impregnating material (not inert to an electrolyte) isprotected from the bulk of the electrolyte by an inert material barrier.

Optionally also the impregnating lug material may be a material which iselectrically conductive but substantially inert to a battery electrolytesuch as a Pb acid battery electrolyte such as titanium.

The conductive or carbon fibre material may have a thickness (transverseto a length and width or in plane dimensions of the electrode) manytimes such as about 10, 20, 50, or 100 times less than the or any inplane dimension of the electrode. The thickness may be less than about 5mm or less than about 3 mm or less than about 2 mm or less than about1.5 mm or about or less than about 1 mm or about 0.2 mm for example.Each of the in plane length and width dimensions of the electrode may begreater than about 50 or about 100 mm for example. Such electrodes havea planar form with low thickness. In preferred forms the electrode issubstantially planar and has a dimension from a metal lug for externalconnection along at least one edge of the electrode less than about 100mm or less than about 70 mm, or less than about 50 mm, or about 30 mm orless for example (with or without a transverse/macro-scale currentcollector). Alternatively such a planar form may be formed into acylindrical electrode for example.

Continuous Lug Manufacture

In accordance with the invention, to enable fast high volume manufactureof multiple electrodes, continuous fibre material is unwound from a rollof many meters of the material for example, is moved continuously or atleast with a stepped movement, past a pressure injection stage, at whichthe lug material is pressure impregnated into the fibre material by aseries of pressure injection pulses. Multiple pressure injection pulsesmay inject lug material into different adjacent portions of the fibrematerial but to form a continuous lug along the lug zone. The lugmaterial penetrates into the fibre material preferably from the surfaceor side from which it is injected to an opposite surface or side.Typically the fibre material is in sheet (planar) form. The method ofthe invention may be carried out without containing the lug zone part ofthe fibre material in a die. The length of the fibre material can besubsequently cut across the lug strip to form multiple individualelectrode elements each with a lug for external connection of theelectrode element. Alternatively the pressure injection stage may bemoved along the length of the continuous fibre material. The method ofthe invention may be carried out by applying continuous pressureinjection as the fibre moves past the pressure injection head.

FIG. 4 shows in close up a portion of fibre material 10 with a lug strip11 being formed on it. The fibre material 10 moves during impregnationin the direction of arrow A beneath an injector head while multiplepressure injection pulses inject molten lug material into the fibrematerial as it moves. For example, the fibre material may move on aconveyor which acts as a heat sink, such as a metal conveyor such as ataut metal band or a rotating drum, while multiple pressure injectionpulses inject molten lug material into the fibre material as it moves.The speed at which the material moves beneath the injector head, thevolume of molten lug material injected at each injector pulse or shot,the duration and frequency of the injector pulses, the duration betweeninjector pulses, the temperatures of the fibre material, and of themolten lug material, are co-ordinated so that the molten lug materialimpregnating into the fibre material from each new injector pulse mergeswhile molten with the lug material in the fibre material injected at theprior injector pulse, to form the continuous lug strip 11. This is acontrolled process to ensure that not too much lug material isintroduced such that it spills beyond the limits of the upper or lowersurfaces of the fibre material, or beyond the desired path within thefibre material.

In FIG. 4 the circles along the length of lug strip 11 eachschematically indicate lug material injected by sequential injectorpulses. The lug material that has been injected by these sequentialpulses are each individually electrically and/or mechanically connectedand/or linked to provide a continuous lug strip. This strip is largelyimpervious to the outside environment. To enable this connection betweeneach of the sequential pulses, for example the duration of each pressureinjection pulse may be in the range about 0.1 to about 2 seconds, orabout 0.1 to 1 second, or about 0.1 to about 80 milliseconds, or about0.1 to about 50 milliseconds, or about 0.1 to about 30 milliseconds, orabout 0.1 to about 10 milliseconds, and for example injector pulses mayseparated by an interval of about 0.1 to about 2 seconds, or about 0.1to 1 second, or about 0.1 to about 80 milliseconds, or about 0.1 toabout 50 milliseconds, or about 0.1 to about 30 milliseconds, or about0.1 to about 10 milliseconds, and when the rate of relative movementbetween the fibre material and pressure injection stage is in the rangeabout 0.01 m/s to 10 m/s, or about 0.01 m/s to 8 m/s, or about 0.01 m/sto 5 m/s. In other embodiments the rate of the pressure pulses isgreater than 1 Hz, greater than 5 Hz, greater 10 Hz or greater than 20Hz. In other embodiments the series of pulses per 0.1 m length of lugzone when moving in the machine direction can be within the range 1pulse/0.1 m to 200 pulses/0.1 m, or within the range 5 pulses/0.1 m to150 pulses/0.01 m, or within the range 10 pulses/0.01 m to 125pulses/0.01 m, or between 20 pulses/0.01 m to 100 pulses/0.01 m, orbetween 30 pulses/0.01 m to 90 pulses/0.01 m.

As the injected lug material is injected it cools largely by conductionto the heat sink conveyor, and also as it moves away from the injectorhead in the machine direction it cools and solidifies. Thus thecontinuous solid lug strip 11 impregnated into the fibre material isformed along the length of the fibre material. The continuous lug stripmay for example have a width in the range about 2 to about 150 mm. Thelug strip may be formed along or near one or both opposite long (in themachine direction) edges of the fibre material and/or centrally in thefibre material, and the length of fibre material cut not onlytransversely into individual electrode segments but also lengthwise. Thetransverse/macro-scale current collector if also provided may forexample have a width in the range about 2 to about 150 mm. By way ofexample, with respect to the temperatures of the fibre material, heatsink conveyor, and molten lug material, with the initial temperatures ofthe fibre material and band at 15 deg C., then superheating of themolten lug material, if it was Pb, may be to about 25 deg C. above themelting point of Pb, but could be up to 150 deg C. above the meltingpoint.

In at least some embodiments the pressure of each pressure injectionpulse is higher at or towards an end of the pulse than at or towards astart of each pulse. At each injector pulse the first lug materialimpregnating into the fibre material may begin to solidify and thusbecome less liquid, and if the latter portion of the lug materialinjected by the same pulse is pushed into the material with higherpressure it will aid in impregnating the lug material further into thefibre material.

FIG. 5 is a schematic cross-section view of fibre material 10 passingbeneath a pressure injection head 12 having an outlet orifice 13, andFIG. 6 is a larger schematic cross-section view of a pressure injectionstage. Each orifice 13 may for example have an area to deliver less thanor equal to 1 cm3 of molten material. The injector head may contact thesurface of the fibre material 10 moving past it or even slightlycompress it as shown, for example by about 10-20% of its free depth, orbe spaced above by for example not more than 10 mm from the surface ofthe fibre material. Compression of the fibre material by the injectorhead may assist in limiting excessive spread of molten Pb across the topsurface of the fibre material and instead assists the molten leadentering into the fibre material.

FIG. 7 is a schematic plan view of fibre material 10 entering andexiting a pressure impregnation stage 14 in one embodiment. FIG. 8 is aschematic plan view of fibre material 10 entering and exiting a pressureimpregnation stage 14 in another embodiment. The fibre material moves inmachine direction A. In the pressure impregnation stage 14 of theembodiment of FIG. 7 a continuous lug strip 11 is formed along onelengthwise edge of the fibre material, also with spaced lug extensions 3beyond the edge of the fibre material. The broken lines across the fibrematerial and lug strip indicate where it will subsequently be cut toform individual electrode elements. In the pressure impregnation stage14 of the embodiment of FIG. 8 continuous lug strips 11 are formed alongboth lengthwise edges of the fibre material, optionally also with spacedlug extensions 3 beyond both edges of the fibre material. Alternativelythe lug extensions may be cut out by a separate cutting machine such asa stamping machine that is provided in line or separately to the lugforming machine. The lug strips may further undergo a trimming stage toremove any excess to form a desirable lug size and shape Any suchtrimmed lug material from the trimming and/or additional cutting stageto form the lug extensions, may be captured by a reticulation systemthat captures the removed trimmings and conveys the trimmings back intotank holding the molten metal to be reused.

Also in the embodiment of FIG. 8 the pressure injection stage forms lugstrips 18 transversely across the fibre material between lug strips 11along the lengthwise edges of the fibre material. In a variant of theembodiment of FIG. 7 such transverse lug strips 18 may extend from theedge lug strip along the lengthwise edge to the opposite edge of thefibre material, or part way across the width of the fibre material.Referring again to FIG. 8, the lug strips 11 along the lengthwise edgesof the fibre material may be formed by outermost injection orifices ofthe injection stage 14 schematically indicated at a and z through whichlug material is injected near continuously to form the edge lug strips11, while the spaced transverse lug strips 18 may be formed by multipleinjection orifices b-y between, through which lug material is injectedonly periodically as the fibre material moves beneath the injectionstage. When in operation, all operate to inject lug material at the sametime for the same duration, and the injection orifices b-y are spacedfrom each other, so that the lug material impregnated into the fibrematerial by each simultaneously, merges and solidifies to form a solidstrip across the fibre material width.

FIG. 6 is a schematic cross-section view of a pressure impregnationstage. Similar reference numerals indicate the same parts as referred toabove. Molten metal to be injected into the fibre material 10 throughorifice 13 is forced under pressure through the orifice by a pistonreciprocating within chamber 15. One piston stroke injecting a setvolume of lug metal into the fibre material may comprise one ‘pulse’ ofthe injector. The injector system may be arranged to increase theinjection pressure so that the injection pressure of the metal into thefibre is higher at or towards an end of the pulse than at or towards astart of each pulse. For the simple single valve mechanical system shownin FIG. 5, the closing of the valve takes an appreciable fraction of thecycle time, and the molten metal leaks back through the valve at areducing rate until it is shut. Thus the available pressure in the spaceabove the injector orifice due to the piston movement graduallyincreases to a maximum as the valve closes.

FIGS. 13 to 18 show an embodiment of a lug forming machine. In thisembodiment the machine comprises side by side pressure injectors 201 and202 to form a continuous lug along opposite lengthwise edges of thecontinuous fibre material as it passes through the machine. Theinjectors are mounted above a conveyor in the form of rotating drum 500,all carried by frame 203. The drum conveyor 500 has a width across anaxis of rotation equal to or greater than the width across the machinedirection of the fibre material so that the drum supports the full widthof the fibre material.

In operation the fibre material passes through a gap between therotating drum 500 and pressure injection heads 201 and 202, as pressureinjection pulses from the injector heads 201 and 202 impregnate lugmaterial into the fibre material along either edge to form a continuouslug along each edge. FIG. 16 is an enlarged schematic verticalcross-section view along line II-II of FIG. 13 and shows in close up aportion of fibre material 100 with a lug strip 101 being formed on it.The fibre material 100 moves during impregnation in the direction ofarrow D beneath the injector head and is supported by the rotating drumwhich also acts as a heat sink conveyor to rapidly cool the molten Pb tocool it rapidly as it exits the gap.

Additionally, FIG. 16 shows the operating parts of injector 201/202 ingreater scale. Injector piston 207 moves reciprocally in cylinder 210 inpiston block 208 as indicated by arrow G and at each downward strokepushes molten lug material from heated reservoir 209 which fillscylinder 210, through port 211 until piston 207 seats against valve seat212 which then closes port 211. The lower surface of foot or injectorhead 215 is curved with a radius to match the drum 500 so that the fibrematerial is held in a gap between the injector head 215 and drum 500 andmay be compressed slightly, such as for example to about 80% of freethickness of the fibre material, between the two as described. Heaters501 may be provided in the block 208 to ensure that the block ismaintained at a temperature that does not partially cool or freeze themolten material in the cylinder or port. Referring also to FIG. 18,molten lug material exits from port 211 into chamber 213 provided ininjector head 215. The molten lug material flows around plate 214provided to ensure an even distribution of the molten flow to allinjector outlet orifices 217, and from outlet orifices 217 into part ofthe fibre material and into the void adjacent the fibre material to formboth a composite zone of lead and fibre and a solid lead zone, thattogether form a lug zone. As the piston moves upwardly before the nextdownward stroke molten Pb refills the cylinder 210 from reservoir 209,before the piston moves downwardly at the next injection pulse. MoltenPb exiting the orifices 217 impregnates the fibre material and theadjacent void passing beneath the injector 202, and rapidly cools toform the continuous lug as the material exits the space between the drum500 and the injector head 201. The system requires temperature controlof the block 208 and injector head 215 and the drum 500 to ensure themolten lead flow freezes or solidifies sufficiently quickly downstreamfrom the injection/casting point so as to create a barrier to theupstream molten lead, but does not freeze too quickly so as to result inblockages underneath the injection/casting point.

FIG. 19 is similar to FIG. 16 and FIG. 20 is similar to FIG. 18 butfurther enlarged, and FIGS. 19 and 20 show the operating parts of analternative embodiment of injector 201/202. Unless indicated otherwisethe same reference numerals in FIGS. 19 and 20 indicate the same partsas in FIGS. 16 and 18, which operate in the same way. A difference isthat whereas in the embodiment of FIGS. 16 and 18 a single injectorpiston 207 moving reciprocally in cylinder 210 at each downward strokepushes molten lug material through injector head 215 to form both acomposite zone 101 of lead and fibre and a solid lead zone, in the dualflow embodiment of FIGS. 19 and 20 the piston 207 pushes (relativelyhigher pressure) pulses of molten lug material through injector head 215to form the composite zone of lead and fibre and a valve 307simultaneously meters a continuous flow of lower pressure molten lugmaterial through injector head 215 to form the solid lead zone. Thevalve 307 moves in chamber 310, in the same piston block 208, and opensin the direction of arrow G′ to allow a lower pressure flow of moltenlug material from heated reservoir same 209, through port 311 intochamber 313 provided in the injector head 215 and then from outletorifices 317 b into the void adjacent the fibre material 100 to form asolid lead zone, at the same time that molten lug material driven byreciprocating piston 207 through port 211 flows from outlet orifices 317a into part of the fibre material to form an adjacent composite zone oflead and fibre (instead of through orifices 217 in the embodiment ofFIGS. 16 and 18). Molten material exiting the orifices 317 a impregnatesthe fibre material and molten material exiting the orifices 317 b fillsthe adjacent void, and the molten material rapidly cools as the materialexits the space between the drum 500 and the injector head, to form thecontinuous lug and lug extension along the edge of the fibre material.We have that where the molten material is lead it may be advantageous toreduce possible blocking of the injector orifices that the leadcomprises a minor proportion of Sn, so that the molten materialcomprises a Pb—Sn alloy. The low and high pressure flows aresynchronized with the travel speed of the fibre material tosimultaneously deliver the correct volumes of lead into the edge region101 of the fibre material and the adjacent void to form the solid lugextension. This embodiment comprises a first pressure injector arrangedto impregnate the lug material into a lug zone part of the fibrematerial and a second adjacent pressure injector arranged to deliver thelug material into an adjacent void to form the solid lug extensionadjacent the lug zone part of the fibre material.

The lug forming machine may comprise a fibre material feed system whichdraws the fibre material through the lug forming machine, whichcomprises drivers specifically optional nip rollers 221 past the exitside of the rotating drum in the machine direction which contactopposite faces of the continuous lengthwise lug just formed on the fibrematerial on either side.

In yet alternative embodiments arranged to form a lug along the edge ofthe fibre material and also a solid lug extension continuously along orat spaced intervals along the edge of the lug, after the edge of thefibre material has been impregnated as described above, separatelyformed lug extension(s) may be attached to the lug by for exampleultrasonic welding or soldering together.

The embodiments above have been described above in relation to formingan electrical connection to a fibre material electrode element. Thefibre material of the electrode element may be electrically conductiveas would be required for a negative or positive electrode in a Pb acidbattery for example, or may be non-conductive, for a positive electrodein a Pb acid battery in some cases for example. For example a positiveelectrode may be formed of polyacrylonitrile fibre material (PAN) whichhas been oxidised to become oxidised PAN fibre (OPF) that has not thenundergone carbonisation which would render it electrically conductive.The invention may also be used for forming an electrical connection to afibre material which is not an electrode element, or even more generallyfor impregnating a first material which is not also electricallyconductive, into a fibre material not for forming an electricalconnection to the fibre material but instead for other industrialpurposes, such as for strengthening and/or building purposes.

Battery or Cell Construction

A lug formed on fibre material electrode as described above may alsocomprise a transverse/macro-scale current collector as describedpreviously (for example see at 52 in FIG. 1) formed in the same way asthe lug ie by pressure impregnation into the fibre material asdescribed. Such a transverse/macro-scale current collector may extendfrom the lug zone at any angle to the lug zone across and to anylocation within the electrode zone, to provide an additional macro scalecurrent collecting pathway from the carbon fibre to the metal lug, inaddition to the micro-scale pathways through the carbon fibre materialitself of the lug. While we refer to such a transverse/macro-scalecurrent collector as such it may also be considered a part of the lug,which lug part passes/is impregnated across the material rather thanonly along an edge or edges. Alternatively or additionally a lug formedon a fibre material electrode as described above may also comprise onone or both sides of the fibre material a metal wire or tapeelectrically conductively attached to the electrode material and to thelug, to provide an additional transverse/macro-scale current collectingpathway from the carbon fibre to the metal lug, in addition to themicro-scale pathways through the carbon fibre material itself of thelug. The metal wire or tape may be attached to the fibre material forexample by stitching or sewing with a thread that will not dissolve inbattery electrolyte, or other inert Pb acid battery binding materialthat will hold the current collector in place, such as a resin, cementor potting mix. The metal wire or tape may be pressed into the fibrematerial during manufacture. Alternatively the wire or tape or similarmay be soldered to or printed on the fibre material. The metal wire ortape(s) may be arranged in a sinuous shape on one or both sides of thefibre material, extending continuously between the lug at one edge ofthe electrode, at which edge the wire or tape is conductively connectedto the lug by being embedded in the lug, and at or towards anotherspaced edge of the electrode. Alternatively the wire or tape may extendbetween metal lugs along opposite edges of the electrode or a framearound the electrode. Alternatively again separate lengths of the wireor tape may extend from the lug at one edge to or towards another edgeof the electrode, or alternatively again the wire or tapemacro-conductor as described may comprise a metal mesh attached on oneor both sides of the fibre material. The ends of the wire or tape ormesh may terminate and be embedded in the lug. It is important that whenthe current collector is on the outer surface of the electrode that actsas the negative electrode the current collector is protected from anodicoxidation from the positive electrode. Preferably the wire or tape runsup and down the length of the electrode with equal spacing across thewidth of the electrode without any cross over points, to prevent localhotspots occurring or heat build up in particular areas, and an evencurrent collection across the electrode. Preferably the volume of thewire or tape or mesh or similar transverse/macro-scale currentcollecting system is less than about 15% of the volume of the electrode(excluding the lug or surrounding metal frame or similar).

Typically during battery or cell construction the fibre material isimpregnated with a paste, which in a preferred form comprises a mixtureof Pb and PbO particles of Pb and PbO and a fluid. In some embodimentsthe fluid is water, an acid or an alcohol. Preferably the acid is dilutesulfuric acid. Preferably the alcohol is ethanol. Alternatively thepaste may comprise lead sulphate (PbSO₄) particles and dilute sulphuricacid. In some embodiments the paste at impregnation into the electrodecomprises dilute sulphuric acid comprising between greater than 0% andabout 6%, or between 0.25% and about 5%, or between 0.25% and about4.5%, or between 1% and about 4%, or between 1% and about 3.5%, orbetween 0% and about 2%, or between 0.5 and 2.5% by weight of the pasteof sulphuric acid. The Pb-based particles may comprise milled orchemically formed particles which may have a mean size of 10 microns orless, small enough to fit easily into spaces between the fibres. Thepaste or active material may fill the carbon fibre electrode up to thelug so that the active material contacts or abuts the lug where thefibre enters the lug and electrically connects direct to the lug, notonly at the surface of the fibre material on either side but alsothrough the thickness of the fibre material, and along a major part ofor substantially all the length of the boundary between the lug materialand the non-lug material impregnated fibre material at this boundary, ormay stop short of the lug so that there is a small gap between the pasteand the lug such as a gap of up to about 5 mm for example. In apreferred embodiment the lug is formed so as to have protrusions of thelug such as Pb protrusions, into the active material impregnated intothe carbon fibre material, as described above.

As stated preferably the surface to volume ratio of Pb particles in theactive material is at least about 3 times greater, or preferably about 5times greater, or preferably about 10 times greater, or preferably about20 times greater, than a surface to volume ratio of lug material in thelug zone. Preferably the surface to volume ratio of Pb particles in theactive material is greater than about 2 m²/cm³ or greater than about 1m²/cm³ and the surface to volume ratio of lug material in the lug zoneis less than about 0.05 m²/cm³. The surface associated with molten lugmaterial that has been injected into fibre layers, cooling as it enters,is likely to be similar to the surface area of the fibres that it willcool around, or less. For example, a carbon felt may have an area of thecylindrical surfaces of the fibres equal to around 20 m² per mmthickness for 1 m² of superficial area, which is equivalent to 0.02 m²per cm³ of felt total volume. Thus flowing molten lead around this fibrenetwork will form (by freezing onto the cold fibres first) a leadstructure with branches larger in diameter than the diameter of thefibres ie. the diameter of the branches of this lead-loaded felt mayincrease from 10 microns to around 15 to 20 microns with surface areaperhaps 0.01 m² per cm³ (for higher volume fraction impregnation thesebranches will merge and the surface will decrease even further). Thesesurface areas can be compared with those for the normal active materialwithin a negative electrode in a lead-acid cell. Lead-containing activemass is divided into a lead skeleton that carries current (which is notsusceptible to electrochemical change during charge and dischargecycles) and a much finer mass that is susceptible to change and in factproduces the working electrical currents of the battery. The much finer“energetic active material” may have around 0.3 micron diameterbranches. The skeleton may be very similar to the branches formed bypartial impregnation above, with negligible electrochemical attack.However the surface area of the fine electrochemically active materialmay have (20)/0.3)=70 times the surface area per unit volume of lead,and so suffers almost all the chemical attack. The division between finematerial and coarse skeleton material is around 50/50% in most negativeelectrodes.

General

In a battery typically a lead-acid battery, the positive electrode orelectrodes, the negative electrode or electrodes, or both, may be formedwith a lug in accordance with the method(s) of the invention. Preferablythe current collector material and the fibres thereof are flexible,which will assist in accommodating volume changes of the active materialattached to the current collector material during battery cycling, andthe microscale fibres may also reinforce the active material, bothassisting to reduce breaking off (“shedding”) of active material fromthe electrode in use.

In preferred embodiments the electrode fibres may be inherentlyconductive without requiring coating with a more conductive materialsuch as a metal to increase conductivity, and may be carbon fibres whichmay in some embodiments be treated to increase conductivity. In otherembodiments the electrode fibres may be a less conductive material, thefibres of which are coated with a conductive or more conductive coating.In some embodiments the fibres of the current collector material may becoated with Pb or a Pb-based material. For example the negativeelectrode or electrodes may be coated with Pb and the positiveelectrode(s) coated with Pb and then thereon PbO₂.

The current collector material may be a woven material, a knittedmaterial, or a non-woven material, such as a felt, or a fluidhydro-entangled material. The material may comprise filaments extendingin a major plane of the material with each filament composed of multiplefibres, with optionally connecting threads extending transversely acrossthe filaments to mechanically connect the filaments. The average depthof the material may be at least 0.2 millimeters or at least 1millimeter. At least a majority of the fibres have a mean fibre diameterof less than about 20 microns, or less than about 10 microns.

In some embodiments the fibre material may be carbon fibre materialwhich has been thermally treated at an elevated temperature, for examplein the range 1000 to 4000° C. In some embodiments the fibre material maybe carbon fibre material which has been treated by electric arcdischarge. The carbon fibre material may be electric arc treated bymoving the carbon fibre material within a reaction chamber eitherthrough an electric arc in a gap between electrodes including multipleadjacent electrodes on one side of the material, or past multipleadjacent electrodes so that an electric arc exists between each of theelectrodes and the material.

In some embodiments the fibre material may be carbon fibre material,such as PAN fibre, that has then been oxidised at temperatures frombetween 250 to 600° C. to provide OPF that is not electricallyconductive. Such fibre materials can be used as an electrode element.

In some embodiments the fibre material may be felt or other non-wovenplanar electrode material produced to very low thickness such as forexample 2.5 mm or less thickness by dividing thicker material in plane.That is, the material may be cut in its plane one or more times todivide a thicker non-woven material into multiple sheets of similarlength and width but reduces thickness to the starting sheet.

EXPERIMENTAL Examples 1 and 2

A layer of carbon felt supported on a steel band was fed beneath astationary steel head that had one or more vertical holes drilledthrough it. Molten lead was held above these holes and could passthrough them to the felt as it passed beneath, as shown in FIGS. 3 to 5.3 L of lead was heated in a cylindrical container so that the leadtemperature could be held to within 1 deg C. of a desired temperatureabove the lead melting temperature. A valve was situated between thepool of lead and the holes, and could be opened and shut to allow shortpulses of lead to pass through them (see FIG. 4 for the case of onehole). The head of this valve contacted a matching seat to close off theflow, and could be raised and lowered from the top of the apparatusthrough axial movements of a stem that passed through the lead pool. Thestem was kept central to the valve by three bearings along its lengthand was attached at its top to a reversing mechanism that allowed thevalve to open briefly once in every rotation of the mechanism. Thefrequency of the mechanism could be adjusted, as also could the durationof the opening. The mechanism was powered by a machine that had amaximum frequency of a push-pull cycle of around 50 Hz. The top of thestem was held down by a compression spring but was lifted to open thevalve towards the top of the movement of the machine, at a position thatcould be adjusted by a single spacer threaded in opposite directions atits two ends.

Example 1

A simple single orifice of diameter 0.5 mm was used, injecting into a2.5 mm thick layer of arc-treated felt with a volume fraction of carbonof 4.2% (mass of carbon per unit area 180 g/m2). The reversingmechanism, in this case a jig-saw, was operated at 50 Hz, so that 50short pulses of lead penetrated the felt each second. The felt wasadvanced at the rate of 40 mm/s and was compressed by the head as it waspassed under. The thickness of the lead composite formed by theinjection was 1.3 mm. FIGS. 9A and 9B are images of the top side andunderside of a section of the carbon fibre felt with the Pb lug stripformed therein. They show the path of the lead infiltration across thefelt, first (a) viewed from the side of the orifice and second (b)viewed from the underside. The felt was carried on a steel belt that wasat room temperature before the lead was injected into the felt above it.The belt thus cooled the felt from the underside. It can be seen fromthe figures that the lead penetrated the felt throughout the visibleextent of the path, with the successive pulses joining together.

Example 2

This example illustrates the use of multiple injection ports. 3 holeswere made in the head each of diameter 0.5 mm, allowing lead pulsedflows from each hole. The feed rate of the felt was 40 mm/s and therepetition rate of pulses was 50 Hz. Under these conditions theinjection from all holes also joined well with those next to them,making a wider injection, about 20 mm wide under the condition used,with thickness 1.3 mm. Cutting out a small area of the path andmeasuring the dimensions and mass allowed one to calculate the voidage,by subtracting both the volume of the carbon (estimated from the knownvolume per m²) and the volume of the lead (estimated from the mass oflead and the density of lead). FIGS. 10A and 10B are images of theunderside and top side of part of the Pb lug strip. The voidage of thissample was 12±2%. In the FIG. 10B top surface image shallow contours arespaced a little shorter than 1 mm apart, indicating where successiveinjections have come together (expected spacing 40/50=0.8 mm). The topof the sample is clear of carbon. A thin cover of carbon remains on thetop of the track after infiltration, but is easily removed e.g. by lightscratching. It appears that any loose small pieces of carbon within thefelt rise to the top during infiltration and this is what is observedbefore the samples are handled. FIG. 11 is an SEM image of the undersideof part of a Pb lug strip formed on a carbon fibre felt from which itcan be seen that Pb has impregnated fully through the carbon fibrematerial.

The driving force for the pulse flow was initially thought to beprovided partly from the static head of the lead at the orifice. Nopressure was applied above the pool of lead in the above examples, sothis static head was that of 300 mm height of lead, i.e. 33 kPa. Howeverwhen the valve was left open without pulsing the valve, the penetrationof lead into the felt was negligible. Also no extra flow into the feltwas observed when the opened period of the valve was increased beyondabout 10% of a full cycle. Thus under these static head conditions, thesignificant effective infiltrating pressure appeared to be from thepumping action of the valve head. An analysis of the fluid flow duringvalve motion was then made. From this analysis the downward movement ofthe head towards closing increased the pressure above the orifice.Taking account of back leakage through the closing annular sealingportion of the valve (see FIG. 6), and using a turbulent pressure dropacross both the injection orifice and annular sealing area (of onekinetic head), one can estimate the profile of pressure and injectionvelocity during the closing portion. This model shows that pressures oftens of bar were generated towards the end of each pulse. This generatedpressure is dropped over both the injector orifice and the rapidlyfilling felt. It is expected that a significant fraction of the totalpressure drop to atmosphere is across the partly filled felt andtherefore this high pressure is effective in adequately filling the feltand achieving a small remaining voidage.

FIG. 12A is an SEM image of a cut through the Pb lug strip (alone)formed on carbon fibre felt and FIG. 12B is a higher magnification SEMimage than FIG. 12A, from which it can be seen that Pb has impregnatedaround and between individual fibres. This shows a low voidage.

The foregoing describes the invention including preferred forms thereofand alterations and modifications as will be obvious to one skilled inthe art are intended to be incorporated in the scope thereof as definedin the accompanying claims.

The invention claimed is:
 1. The method for forming an electricalconnection to a fibre material electrode element, which comprises:moving continuously or in a stepped movement a length of fibre materialrelative to a pressure injection stage or vice versa; and by thepressure injection stage pressure impregnating without containing thefibre material in a die an electrically conductive molten lug materialinto a lug zone part of the fibre material during the relative movementbetween the fibre material and the pressure injection stage, to surroundand/or penetrate fibres of the fibre material and so that the molten lugmaterial newly impregnating into the fibre material merges while moltenwith the lug material in the fibre material injected immediately priorto form a continuous lug strip of the impregnated material in a lug zonepart of the fibre material, said lug zone part of the fibre materialhaving a width transverse to a length of the fibre material less than agreater width of the fibre material.
 2. The method according to claim 1including pressure impregnating by applying continuous pressure to theelectrically conductive molten lug material into the lug zone part ofthe fibre material as the fibre moves past the pressure injection head.3. The method according to claim 1 including moving the fibre materialrelative to the pressure injection stage or vice versa by carrying thefibre material on a heat sink conveyor.
 4. The method according to claim1 including subsequently cutting the length of the fibre material acrossthe lug strip to form multiple individual electrode elements each with alug for external connection of the electrode element.
 5. The methodaccording to claim 1 wherein the fibre material has an averageinterfibre spacing less than about 200 microns.
 6. The method accordingto claim 1 including forming a lug extension beyond an edge of the fibrematerial.
 7. The method according to claim 1 wherein the fibre materialis a carbon fibre material.
 8. The method according to claim 1 whereinthe fibre material comprises an electrically non-conductivepolyacrylonitrile fibre material.
 9. The method according to claim 1wherein the lug material is Pb or a Pb alloy, Zn or a Zn alloy, or Cd ora Cd alloy, Al or Al alloy.